Acetone Ketyl Radical Research Articles

Time-resolved electron paramagnetic resonance spectrometer based on ultrawide single-sideband phase-sensitive detection.

A time-resolved electron paramagnetic resonance (TREPR) method with 40ns time resolution and a high sensitivity suitable for the detection of short-lived radicals under thermal equilibrium is developed. The key is the introduction of a new detection technique named ultrawide single sideband phase sensitive detection (U-PSD) to the conventional continuous-wave EPR, which remarkably enhanced the sensitivity for the detection of broadband transient signals compared with the direct detection protocol. By repeatedly triggering a transient kinetic event f(t) (e.g., by laser flash photolysis) under a 100kHz magnetic field modulation with precise phase control, this technique can build an ultrawide single sideband modulated signal. After single sideband demodulation, the flicker noise-suppressed signal f(t) with wide bandwidth is recovered. A U-PSD TREPR spectrometer prototype has been built, which integrated timing sequence control, laser flash excitation, data acquisition systems, and the U-PSD algorithm with a conventional continuous-wave EPR. It exhibited excellent performance in monitoring a model transient radical system, laser flash photolysis of benzophenone in isopropanol. Both the intense chemically induced dynamic electron polarization signals and the much weaker thermal equilibrium EPR signals of the generated acetone ketyl radical and benzophenone ketyl radical were clearly observed within a wide timescale ranging from sub-microsecond to milliseconds. This prototype validated the feasibility of the U-PSD technique and demonstrated its superior performance in studying complex photochemical systems containing various transient radicals, which complements the established TREPR techniques and provides a powerful tool for deep mechanistic understandings, such as in photoredox catalysis and artificial photosynthesis.

Efficient Photoredox Cycles to Control Perylenediimide Self-Assembly.

Photoreduction of perylenediimide (PDI) derivatives has been widely studied for use in photocatalysis, hydrogen evolution, photo-responsive gels, and organic semiconductors. Upon light irradiation, the radical anion (PDI⋅- ) can readily be obtained, whereas further reduction to the dianion (PDI2- ) is rare. Here we show that full 2-electron photoreduction can be achieved using UVC light: 1) in anaerobic conditions by 'direct photoreduction' of PDI aggregates, or 2) by 'indirect photoreduction' in aerobic conditions due to acetone ketyl radicals. The latter strategy is also efficient for other dyes, such as naphthalenediimide (NDI) and methylviologen (MV2+ ). Efficient photoreduction on the minute time-scale using simple LED light in aerobic conditions is attractive for use in dissipative light-driven systems and materials.

Laser flash photolytic generation of radical ions of carotenoids in organic solvents. Studies of their subsequent fates, including formation of stable carotenoid sigma dimer radical anion (CAR)2[rad

In this study, time-resolved laser flash photolysis technique (LFP) was used to generate and study extraordinary stable transients formed following the decay of radical anions of canthaxanthin (CAN) and astaxanthin (ASTA). The radical anions were obtained via one-electron reduction of CAN and ASTA by acetone ketyl radical (AC−) in various solvents. At room temperature, the decay of CAN− (λmax = 870 nm) and ASTA− (λmax = 1000 nm), in acetonitrile (ACN), led to the formation of indefinitely stable colored transients (blue-green for CAN and navy blue for ASTA) absorbing at shorter wavelengths (λmax = 690 nm and 720 nm, respectively) relative to their corresponding radical anions. Rapid quenching by oxygen was observed indicating the radical nature of these transients, which was further confirmed by EPR spectroscopy. By employing EPR spectroscopy, LFP technique, and UV–visible absorption measurements, these extraordinary stable transients were identified as sigma-dimer radical anions ((CAR)2−) formed via the dimerization of the parent carotenoid (CAR) with its radical anion (CAR−). The suggested structures of these dimers were postulated using DFT calculations, which indicated that the unpaired electron is delocalized over the entire molecule. This result is extremely important because of the paucity of reports on dimer radical anions in solution.

A novel luminol chemiluminescence induced by photoexcited ketones: A selective determination method for acetone in wastewater

It has been recently confirmed that photoexcited ketones such as acetone promote the chemiluminescence (CL) reaction of luminol and its analog, L-012. Using this finding, a selective determination method for acetone was developed herein based on HPLC separation, online UV irradiation, and subsequent luminol CL detection. Various conditions, including the type of luminol reagent, the use of organic solvents as eluent modifiers, and the reaction pH, were investigated to elucidate the CL reaction mechanism. The results showed that the CL reaction of luminol is caused by an acetone ketyl radical produced from the photoexcited acetone. The performance of the novel acetone determination method was evaluated by its application in water quality assurance in water treatment plants. The method detection limit and the method quantification limit of acetone were 0.03 and 0.08 µM, respectively. A linear range was obtained in the concentration range of 0.1–200 µM. The range of recovery in the wastewater and seawater samples (n = 5) fortified with 5.0 µM acetone was 87–108%. These results demonstrate that the new luminol CL system is useful for its sensitivity and selectivity.

Carotenoid radical ions: A laser flash photolysis study

Laser excitation of a single precursor, namely 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMP), has been used for generating the radical cations and radical anions of various carotenoids in methanol. In the presence of oxygen, laser excitation of HHEMP undergoes an efficient α-cleavage reaction (Norrish type I) to form acyl radicals, which react with O2, in a nearly diffusion-controlled reaction, to form their corresponding strong oxidizing acylperoxyl radicals (RO2•) (E = ~1.1 V (v SHE)), which are capable of oxidizing almost all carotenoids. Under argon-saturated conditions and in the presence of strong base (0.01 M NaOH or tetrabutylammonium hydroxide (TBAOH)), the initially formed 2-hydroxy-2-propyl radical (ACH•), generated after LFP of HHEMP, is deprotonated to form the strong reducing acetone ketyl radical (AC•-) (E {acetone/ AC•-} = −2.1 V (v SHE)), which is capable of reducing all carbonyl-containing carotenoids. To validate this new proposed approach, retinal and β-apo-8′-carotenal (APO), with known spectroscopic data, were investigated in methanol, acetonitrile and tetrahydrofuran (THF). In addition, the radical ions of newly investigated carotenoids, namely 4-oxo-β-apo-15′-carotenoic acid (4-oxo-15′), crocetindial, 4-oxo-β-apo-10′-carotenoic acid ethyl ester (4-oxo-10′) and 4-oxo-β-apo-8′-carotenoic acid ethyl ester (4-oxo-8′) have been reported. Moreover, the scope of this approach has been extended to investigate the radical ions of chlorophyll b.

Reconciling Disparate Models of the Involvement of Vinyl Radicals in Cobalamin-Mediated Dechlorination Reactions

Inner-sphere (nonradical) and outer-sphere (radical-based) mechanisms have been suggested for cobalamin-mediated dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). In this study, the role of free vinyl radicals was investigated using deuterated radical traps: d(8)-isopropanol and d(8)-tetrahydrofuran. For both substrates, addition of trap resulted in production of deuterated dechlorination products, and higher concentrations of trap resulted in increased amounts of deuterated products. However, only a finite proportion of the products were trappable: 8% of the PCE-derived products and 86% of the TCE-derived products result from free radicals. The data show that the reaction does not proceed solely by either an inner-sphere or an outer-sphere mechanism and led to the hypothesis that caged radical intermediates were involved in the mechanism. The untrappable fraction of products are hypothesized to result from in-cage reactions. This hypothesis was investigated using d(5)-glycerol as a radical trap and viscogen. Although increased viscosity resulted in decreased formation of free-radical-derived products, consistent with the cage hypothesis, these data were inconclusive. The role of d(8)-isopropanol in enhancing the production of radicals in this system via an acetone ketyl radical chain mechanism was also investigated, and no evidence for such an effect was found.

Involvement of triplet state in the photodissociation of hydrogen peroxide: experimental evidence from time-resolved EPR study

The dissociation of photoexcited hydrogen peroxide to generate a pair of hydroxyl radicals is generally believed to take place in a repulsive electronic singlet state. The results presented here, based on time-resolved EPR experiments on the spin polarisation pattern of the acetone ketyl radical (CH3)2C•OH, generated on photodissociation of H2O2 in 2-propanol with a 248 nm laser light, strongly indicate significant involvement of a repulsive triplet state of excited hydrogen peroxide.

On the Mechanism of Reaction of Radicals with Tirapazamine

Ketyl radicals produced by photolysis of ketones or di-tert-butyl peroxide (DTBP) in alcohol solvents react rapidly with tirapazamine (TPZ). The acetone ketyl radical (ACOH) reacts with TPZ with an absolute second-order rate constant of (9.7 +/- 0.4) x 108 M-1 s-1. The reaction kinetics can be followed by monitoring the bleaching of TPZ absorption at 475 nm or the formation of a reaction product which absorbs at 320 and 410 nm. The ACOD radical reacts with TPZ in 2-propanol-OD with an absolute rate constant of (6.7 +/- 0.5) x 108 M-1 s-1, corresponding to a kinetic isotope effect (KIE) of 1.4. Deuteration of the radical on carbon (ACOH-d6) retards the reaction of the radical with TPZ even further (absolute rate constant = (4.8 +/- 0.04) x 108 M-1 s-1). This result corresponds to a KIE of 2.0. Radicals derived from dioxane and diisopropyl ether by flash photolysis of DTBP in ethereal solvent react with TPZ more slowly than do ketyl radicals. It is concluded that ketyl radicals react, in part, with TPZ in organic solvents by transfer of a hydrogen atom from the OH and CH3 groups of the ketyl radical to the oxygen atom at the N4 position of TPZ to form acetone or acetone enol and a radical derivative of TPZ (TPZH). The latter species absorbs at 320 and 405 nm, has a lifetime of hundreds of microseconds in alcohol solvents, and decays by disproportionation to form TPZ and a reduced heterocycle. The reduced heterocycle eventually forms a desoxytirapazamine by a polar mechanism. The results are supported by density functional theory calculations. It is proposed that dioxanyl radical will also react, in part, with TPZ by transfer of a hydrogen atom from the carbon adjacent to the radical center to the oxygen atom at the N4 position of TPZ. This produces the enol ether and the previously mentioned TPZH radical. It is further posited that ether radicals react a bit more slowly than ketyl radicals because they lack the second mode of hydrogen transfer (from the OH group) that is present in the ACOH radical. Our data are permissive of the possibility that ether radicals add to TPZ at a rate that is competitive with beta-hydrogen atom transfer.

Studies of carotenoid one-electron reduction radicals

The relative reduction potentials of a variety of carotenoids have been established by monitoring the reaction of carotenoid radical anion (CAR1 − ) with another carotenoid (CAR2) in hexane and benzene. This order is consistent with the reactivities of the carotenoid radical anions with porphyrins and oxygen in hexane. In addition, investigation of the reactions of carotenoids with reducing radicals in aqueous 2% Triton-X 100, such as carbon dioxide radical anion ( CO 2 - ), acetone ketyl radical (AC − ) and the corresponding neutral radical (ACH ), reveals that the reduction potentials for β-carotene and zeaxanthin lie in the range −1950 to −2100 mV and those for astaxanthin, canthaxanthin and β-apo-8′-carotenal are more positive than −1450 mV. This illustrates that the presence of a carbonyl group causes the reducing ability to decrease. The radical cations have been previously shown to be strong oxidising agents and we now show that the radical anions are very strong reducing agents.

Kinetic and spectral studies on transient species formed in pulse radiolysis of 2,6-diacetylpyridine in aqueous solutions

Reactions of e − aq, OH radicals, H-atoms and reducing (CH 3) 2C OH/CO 2 − radicals with 2,6-diacetylpyridine were studied using pulse radiolysis technique in aqueous solutions. At pH 9.2, e − aq reaction with 2,6-DAP ( k = 2.1 × 1 0 10 dm 3 mol - 1 s - 1 ) was found to generate a transient species having absorption maxima at 320 and 420 nm. Reaction of e − aq with 2,6-DAP was also studied at pH∼13.3. Semi-reduced species formed at pH∼13.3 were found to transfer electron to methyl viologen with 100% efficiency ( k = 2.9 × 1 0 9 dm 3 mol - 1 s - 1 ), whereas at pH 9.2 an equilibrium was attained. Making use of this equilibrium, the one-electron reduction potential of 2,6-DAP has been estimated to be −0.513 V vs. NHE at pH 9.2. Following the change in absorption spectra of semi-reduced species at pH 9.2 and ∼13.3, p K a for the protonation of 2,6-DAP radical anion (2,6-DAP − /2,6-DAPH ) has been determined to be ∼11.9. Acetone ketyl radicals were found to transfer electron to 2,6-DAP with rate constants of 2×10 9, 6.3×10 7 and 1.2 × 1 0 8 dm 3 mol - 1 s - 1 at pHs∼13.3, 9.2 and 1, respectively. By making use of the changes in the absorbance of species formed in reaction with acetone ketyl radicals with 2,6-DAP, p K a for the protonation of 2,6-DAPH (2,6-DAPH /2,6-DAPH 2 + ) has been estimated to be ∼1.5. H-atoms were found to react with 2,6-DAP by addition pathway rather than electron transfer. OH radical reaction with 2,6-DAP ( k = 1.8 × 1 0 9 dm 3 mol - 1 s - 1 ) at pH 9.2 was found to generate transient species having absorption maxima at 310 and 400 nm. At pH 1 also, the spectrum of the species formed in OH radical reaction with 2,6-DAP was similar to that formed at pH 9.2 whereas reaction of O − radicals with 2,6-DAP ( k = 1.8 × 1 0 9 dm 3 mol - 1 s - 1 ) generated a transient species whose absorption spectrum was different.

Redox reactions of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) in aqueous solution

Pulse radiolysis technique has been employed to study the reactions of oxidizing (OH, N3) and reducing radicals (e−aq, CO2−, acetone ketyl radical) with 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) at different pH. Hydroxyl radicals react mostly by addition reaction forming radical adducts (λmax=420 nm) and the oxidation is only a minor process even in the alkaline region. The reaction with azide radicals produced phenoxyl radicals (λmax=340 nm), which are formed on fast deprotonation of solute radical cation. Using PMZ+/PMZ and ABTS−/ABTS2− as the reference couple, different methods are employed to determine the one-electron reduction potential of o-vanillin and the average value is estimated to be 1.076±0.004 V vs. NHE at pH 6. The phenoxyl radicals of o-vanillin were able to oxidize ABTS2− quantitatively. The eaq− is observed to react with o-vanillin with rate constant value of 2×1010 dm3 mol−1 s−1. CO2− and acetone ketyl radical are also observed to react with o-vanillin by electron transfer mechanism and showed the formation of transient absorption bands with λmax at 350 and 390 nm at pH 4.5 and 9.7, respectively. The pKa of the one-electron reduced species was determined to be 8.1. The results indicate that the aldehydic group is the most preferred site for electron addition.

Redox reactions of 2-hydroxy-3-methoxybenzaldehyde ( o-vanillin) in aqueous solution

Pulse radiolysis technique has been employed to study the reactions of oxidizing ( OH, N 3 ) and reducing radicals (e − aq, CO 2 − , acetone ketyl radical) with 2-hydroxy-3-methoxybenzaldehyde ( o-vanillin) at different pH. Hydroxyl radicals react mostly by addition reaction forming radical adducts ( λ max=420 nm) and the oxidation is only a minor process even in the alkaline region. The reaction with azide radicals produced phenoxyl radicals ( λ max=340 nm), which are formed on fast deprotonation of solute radical cation. Using PMZ + /PMZ and ABTS − /ABTS 2− as the reference couple, different methods are employed to determine the one-electron reduction potential of o-vanillin and the average value is estimated to be 1.076±0.004 V vs. NHE at pH 6. The phenoxyl radicals of o-vanillin were able to oxidize ABTS 2− quantitatively. The e aq − is observed to react with o-vanillin with rate constant value of 2×10 10 dm 3 mol −1 s −1. CO 2 − and acetone ketyl radical are also observed to react with o-vanillin by electron transfer mechanism and showed the formation of transient absorption bands with λ max at 350 and 390 nm at pH 4.5 and 9.7, respectively. The p K a of the one-electron reduced species was determined to be 8.1. The results indicate that the aldehydic group is the most preferred site for electron addition.

One-electron reduction of 1,2-dihydroxy-9,10-anthraquinone and some of its transition metal complexes in aqueous solution and in aqueous isopropanol–acetone-mixed solvent: a steady-state and pulse radiolysis study

One-electron reduction of 1,2-dihydroxy-9,10-anthraquinone (DHA) and its complexes with Cu(II), Ni(II) and Fe(III), by acetone ketyl radical, (CH 3) 2C·OH, was carried out in aqueous solution and in aqueous isopropanol acetone mixed solvent using both steady-state gamma radiolysis and pulse radiolysis techniques. The rate constants for the reduction of DHA at different pH values by the ketyl radical are in the order of ∼10 9 dm 3 mol −1 s −1, whereas those for the metal complexes are comparatively less. These rate constants are, however, in conformity with the one-electron reduction potentials of the ligand in free DHA and in its metal complexes. Decay kinetics of the one-electron reduced semiquinones of the free ligand and its metal complexes suggest disproportionation of the semiquinone in the case of the free ligand and intermolecular electron transfer from the co-ordinated semiquinone radical to the metal centre in the case of the metal complexes.

Nature of transient species formed during pulse radiolysis of 4-mercaptopyridine in aqueous solutions: Formation of a dimer radical species by one-electron reduction reaction

Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N3• and Br2−•, react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS• /4-PyS− was estimated to be 0.93V vs. NHE by equilibrium reaction with I2−• /2I− couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl2−• and Br2−• radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, eaq− reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.

Kinetic and spectral properties of intermediates formed during pulse radiolysis of 2,6-pyridinedicarbonyl dichloride in aqueous solutions

Reactions of e aq −, H-atoms, OH radicals and some one electron oxidants and reductants with 2,6-pyridinedicarbonyl dichloride (PCC) were studied in aqueous solutions using pulse radiolysis technique. The transient species formed by the reaction of e aq − with PCC at pH 6.8 has two absorption bands with λ max at 300 and 380 nm and is reducing in nature. The semi-reduced species was found to be neutral in nature indicating that the electron-adduct gets protonated quickly. At pH 4.3, the rate constant for e aq − reaction with PCC was found to be higher than that obtained at pH 6.8 indicating that the parent compound is in the protonated form at this pH. The p K a of the parent compound was determined to be 5.3. H-atom reaction with PCC at pH 1 produced a mixture of transient species having absorption bands at 290 and 380 nm. Reaction of acetone ketyl radical and CO 2 −. radical with PCC at pH 6.8 gave a transient spectrum identical to that obtained by e aq − reaction. At pH 1 also, the spectrum of the transient species obtained by the reaction of these radicals with PCC was identical to that obtained at pH 6.8 indicating that the same species is formed at both the pHs. The absorption spectra of the transient species formed by OH radical reaction with PCC at pHs 3.6 and 6.8 were found to have λ max at about 350 nm and a weak band at longer wavelengths. However, the extinction coefficient values were quite different at the two pHs indicating the existence of acid–base conjugate forms of the intermediate species.

Pulse radiolysis study of diphenylcarbazide in aqueous solutions

The semi-reduced species formed by the reaction of e − aq with DPC at pH 6.8 was found to have three absorption bands with λ max values at 320, 360 and 480 nm. It was found to be reducing in nature. H-atom reaction with DPC at pH 2 initially gave a transient species with absorption maximum at 340 nm which can be assigned to the cyclohexadienyl type of radical. This species decayed by first order kinetics to give another transient species with spectrum similar to that obtained by e − aq reaction with DPC. Reaction of acetone ketyl radicals with DPC at pH 2 and 6.8 also gave the same spectrum as obtained by e − aq reaction. The initial OH adduct of DPC at pH 6.8 has absorption maximum at 340 nm (due to hydroxycyclohexadienyl type radical). This species also decayed by first order kinetics to give a semi-oxidised species having an absorption maximum at 480 nm. One-electron oxidants like N 3 radicals also reacted with DPC to give the same species with λ max at 480 nm.

Pulse radiolysis study of dithio-oxamide in aqueous solutions

The reactions of e- aq , H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions using pulse radiolysis technique. The transient species formed by the reaction of e- aq with DTO at pH 6.8 has an absorption band with λ max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species produced by H-atom reaction had a different spectrum with λ max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO 2 radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1-9.2 also has two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1. This means that all these radicals viz. OH, H-atom and (CH 3 ) 2 COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to the presence of oxygen. One-electron oxidizing radicals such as Br2 - and SO 4 radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima at 360 to 520 nm. At acidic pHs, only Br 2 and Cl 2 radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is a resonance stabilized species with the electron delocalized over the -N-C-S bond. This species was found to be neutral and non-oxidizing in nature.

Photochemical generation of acrylate radicals by sensitizing with acetone–propan-2-ol. A laser photolysis Fourier transform electron paramagnetic resonance study

The sensitized generation of acrylate radicals was studied in acrylate–acetone–propan-2-ol solution by using laser photolysis with time-resolved Fourier transform electron paramagnetic resonance (EPR). In addition to the acetone ketyl radical, vinyl-type radicals of various acrylates were observed in the nanosecond and microsecond time scales. Classification as vinyl-type radical structures was underpinned by quantum-chemical calculations. The acrylate radicals were E/A spin-polarized by the CIDEP radical pair mechanism as described. A triplet exciplex is proposed as the precursor state of the acetone–acrylate radical pair. This interpretation is supported by quantum-chemical calculations.

One-Electron Reduction of 3,3,6,6-Tetramethyl-3,4,6,7,9,10-hexahydro-(1,8)-(2H,5H)-acridinedione: A Pulse Radiolysis Study

The radical anion formed on reaction of e aq ¯ with acridinedione dye (ADH) exhibits transient optical absorption bands at λ max = 315, 460, and >780 nm. The bimolecular rate constant for the reaction of e aq ¯ with the dye was determined to be 2.7 × 10 10 dm 3 mol -1 s -1 . It is converted to (ADH 2 • ) on protonation and showed an absorption band at 310 nm. At pH = 1, acetone ketyl radicals are observed to react with the dye with a bimolecular rate constant of 2.3 × 10 8 dm 3 mol -1 s -1 , and the transient optical absorption bands ( λ max = 315, 540 nm) are assigned to (ADH 3 ) •+ . The radical anion (ADH •- ) is a strong reducing agent, with reduction potential = -1.37 V vs NHE, and is able to undergo electron-transfer reactions with methyl viologen (MV 2+ ) and p-nitroacetophenone (p-NAP) with bimolecular rate constants of 4.9 × 10 9 and 6.1 × 10 9 dm 3 mol -1 s -1 , respectively.

Anomalous high reactivity of formyl and acetone ketyl radicals with uracil and its derivatives

CO 2 ·− and ( CH 3) 2 · COH radicals apparently react with uracil and its derivatives, containing two carbonyl groups, with high rate constants ( k=10 10 dm 3 mol −1 s −1). Various mechanistic aspects of such reactions have been probed. The effect of pH and buffer concentration on the initial formation of absorbance points to some keto-enol tautomerism-type fast-reaction between OH − and the substrate, followed by a slower relaxation to the original equilibrium. The radical anions of these compounds react with methyl viologen mainly via an electron transfer reaction with a high rate constant value (4–9)×10 9 dm 3 mol −1 s −1.